Internal combustion engines for vehicles are known, comprising a head with one or more cylinders, inside which the engine cycle takes place, and which are connected with respective combustion chambers of the engine. Moreover, suitable seats are obtained on the aforesaid head, intended to connect the combustion chamber with ports adapted to supply said chamber with a mixture of unburnt fuel and air (“intake ports”), and to remove the burnt gases from said combustion chamber (“exhaust ports”).
The flows from and towards each combustion chamber are controlled by suitable valves acting on the aforesaid seats. In particular, each valve essentially comprises a guide element, secured inside a cavity of the cylinder head of the motor and defining a through seat, and a stem, sliding in opposite directions inside the aforesaid seat and carrying at one end a closing portion for closing the connection between the relative intake or exhaust port and the corresponding combustion chamber.
The opposite end of the stem of the valve projects axially from the relative guide element and is adapted to receive operating forces from a relative control device, for example a cam shaft.
The stem of the valve is axially loaded by a cylindrical helical spring in the direction for closing the connection between the relative intake or exhaust port and the corresponding combustion chamber.
In particular, the spring is mounted coaxially around the valve and is axially interposed between a fixed surface obtained on the cylinder head and a plate secured to the stem of the valve close to or at the end of the stem cooperating with the control device.
Sealing gaskets are normally fitted on valves of the type described above for the lubricating oil normally circulating in engines. These gaskets, in one of the most commonly known forms, comprise a support or reinforcing member, having a substantially tubular or annular shape and made in one single piece of metal material, and an annular seal element, made of an elastomeric material and interposed between the support member and the valve.
In particular, the seal element typically comprises a first portion adapted to cooperate, by means of a radially internal annular surface thereof, with the radially external annular surface of the portion of the guide element in use facing the aforesaid control device, and a second portion adapted to cooperate directly with the valve stem.
Gaskets of the type described above are widely used on all internal combustion engines to control the amount of lubricating oil that flows from the distribution area towards the combustion chambers. An excessive flow of lubricating oil, besides causing an evident excessive consumption of this oil, also causes a deterioration of engine efficiency and a reduction in the performance of the vehicle catalyst. On the other hand, insufficient flow causes an increase in wear and noise of the valves accompanied by the presence of local temperature spikes. These phenomena can cause premature damage to the valves resulting from seizure of the valve stem inside the guide element.
Known gaskets allow, by means of the first portion of the seal element acting on the guide element of the relative valve, the achievement of a static seal, and, by means of the second portion of the seal element cooperating with the stem, the achievement of a dynamic seal. In particular, the static seal must ensure a certain degree of radial compression on the guide element in order to prevent leakage of lubricating oil towards the combustion chambers and at the same time maintain the gasket in position, while the dynamic seal is designed to allow the minimum flow of oil necessary for lubrication of the coupling between stem and guide element.
In particular, the support member comprises a roughly cylindrical retention portion, coupled coaxially on the first portion of the seal element so that this first portion is radially interposed in use between the retention portion and the guide element of the valve.
In order to generate the radial pressure necessary to define the dynamic seal, an elastic ring is commonly mounted on the second portion of the seal element, intended to act directly on the valve stem; this ring has the function of tightening the second portion of the seal element on the stem with a pressure such as to allow minimum leakage of oil to lubricate the guide element—stem coupling.
Although the solution described is functionally valid, it is susceptible to further improvements: in fact, there is the need to reduce the number of components to be managed and fitted to achieve the gaskets of the aforesaid type, in order to also simultaneously reduce the costs of these latter.
Moreover, over time the elastic ring could lose part of its elasticity, thereby compromising the correct operation of the gasket; in fact, it has been noted that this loss of elasticity generally occurs in a shorter time with respect to the normal life cycle of the other components of the gasket.
It must also be mentioned that the elastic ring could become unseated during shipping or assembly on the engine valve.
In order to reduce the total number of components forming the gaskets of known type and to overcome the problem specified above, the U.S. Pat. No. 6,516,769 proposes replacing the elastic ring with a thrust portion of the support member, made in one single piece with the retention portion.
However, this solution does not seem completely satisfactory from the point of view of the coupling to be achieved between the seal element and the support member while fitting the gasket.
Moreover, the need to couple two components with complex shapes tends to set limitations during the design thereof, which could penalize, even only partially, their respective functionality or at least the overall radial dimensions of the gasket.